"This research holds important implications for understanding disorders such as diabetes, heart disease and obesity, and identifies targets for the development of gender-specific therapies," says Jake Lusis, a professor of human genetics who worked on the study.

Writing in the August issue of the journal Genome Research, the researchers say that even in the same organ, scores of genes vary in expression levels between the sexes.

The smallest differences are in brain tissue.

"We saw striking and measurable differences in more than half of the genes' expression patterns between males and females," says Dr Thomas Drake, a professor of pathology.

"We didn't expect that. No one has previously demonstrated this genetic gender gap at such high levels."

Xia Yang, a postdoctoral fellow in cardiology who led the study, says the implications are important.

"Males and females share the same genetic code, but our findings imply that gender regulates how quickly the body can convert DNA to proteins," Yang says. "This suggests that gender influences how disease develops."

In liver tissue, the findings imply male and female livers function the same, but at different rates.

"Our findings in the liver may explain why men and women respond differently to the same drug," Lusis says.

"Studies show that aspirin is more effective at preventing heart attack in men than women. One gender may metabolise the drug faster, leaving too little of the medication in the system to produce an effect."

Yang adds: "Many of the genes we identified relate to processes that influence common diseases. This is crucial, because once we understand the gender gap in these disease mechanisms, we can create new strategies for designing and testing new sex-specific drugs.